soc: qcom: glink_smd_xprt: Remove unnecessary mutual exclusion

Receive command mutual exclusion is required only for the channel open
& close related operations and is not required for any operations relating
to data exchange.

Remove receive command mutual exclusion from the location where it is not
required.

Change-Id: Icebab0b36d71165d895e0fed2e9cfe2c624056b9
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>